There has long been an industrial need for flexible polymers which exhibit good chemical, thermal, and moisture resistance, and which in film-form are relatively impermeable by gases. While various polymers have been developed which display one or more such characteristics, few have been discovered which display most, or all of them. In addition, some of the polymers which do have characteristics which include at least some of those described, are undesirably brittle and unsuited for applications where the material is to be subjected to mechanical stress, or where good substrate adhesion is required. In the electronics industry, for example, the advent of microprocessors, and microcircuitry in general, has created a need for protective films which adhere strongly to the substrates on which they are placed, which are flexible enough to withstand mechanical stresses, which are thermally stable, and which are impermeable to moisture and reactive materials present in the ambient atmosphere to which they are exposed. Further, in the medical field, particularly in connection with devices such as pacemaker wire coatings, there is a need for chemically inert, strongly adherent materials that can be used with such devices as a protective coating. In addition, there are numerous other specialty adhesive and sealant applications which would benefit from polymer compositions having the desirable characteristics described.
In the recent past, considerable interest has been shown in high-energy curable coatings such as polyesters and polyethers capped with acrylate and methacrylate functions, in combination with various low molecular weight acrylate or methacrylate esters. Unfortunately, however, the cross-linked compositions obtainable from such materials reflect the properties of their base polymers, and the latter are commonly deficient in one or more respects relative to the properties sought, as previously described, particularly with respect to flexibility. Attempts have been made to incorporate various polar rubbers such as the fluorocarbons and nitrile rubbers; however, such attempts have not been completely successful. Nonpolar rubbers such as polyisobutylene have not hitherto been used in ultraviolet curable formulations, possibly due to their chemical inertness, a characteristic which interferes with their incorporation into an acrylate network. In addition, even when acrylate or methacrylate capped polyisobutylenes are cross-linked by themselves with UV radiation, they exhibit unacceptable levels of extractable fractions, possibly due to the reduced mobility of the capped polyisobutylenes as the cross-linking reaction proceeds. This apparently limits their ability to enter into the cross-linking reaction and makes them vulnerable to extraction.